The pop star celebrated at the No Name Club in Hollywood with fiancé and "Chicago Fire" actor Taylor Kinney, 34, as well as a slew of celebrity friends. Gaga, who turns 30 on Monday, wore a glittering gold boat neck mini dress with puffy short sleeves and thick black belt, paired with black strappy platform peep-toe pumps and a sparkling Lorraine Schwartz choker.

Swift, who wore a loose-fitting black, shimmering jumpsuit, gave Gaga a huge hug and danced with her and Hudson. She was also seen talking to del Rey and Williams.

"Everyone sang 'Happy Birthday' to Gaga and it was a perfect night," the source added.

Teigen, who wore a black outfit as well, is weeks away from giving birth to her and Legend's first child. She had a lot of energy at the party and she and her hubby shared many kisses, the source told E! News.

The party continued until the early hours of the morning. Hudson, who wore a plunging, half-sheer black dress, left around 4 a.m. alone, another source told E! News exclusively.

She and Jonas, who sported a black tux, arrived at the party separately, the source added. The two had sparked romance rumors last September and have been spotted out together in recent months but have never confirmed a relationship.